Let-off motion for looms



5 Sheets-Sheet 1 @www f..

Feb. 25, 1964 R. HONEGGER LET-OFF MOTION Fox Looms Filed Nov. 14, 1960 Feb. 25, 1964 R. HONEGGER LET-oFF MOTION FOR Looms 5 Sheets-Sheet 2 Filed NOV. 14. 1960 R. HONEGGER LET-OFF MOTION FOR LOOMS Feb. 25, 1964 Filed Nov. 14, 1960 5 Sheets-Sheet 3 y .FWN

| ||||||||l III! R. HONEGGER LET-OFF MOTION FOR LOOMS Feb. 25, 1964 5 Sheets-Sheet 4 Filed Nov. 14, 1960 Feb. 25, 1964 R. HONEGGER 3,122,172

LET-OFF MOTION Foa Looms Filed Nov. 14. 19Go 5 sheets-sheet ls United States Patent O Filed Nov. 14, 195i?, Claims priority, appl Claims.

This invention relates to an automatic let-o motion for looms, by which a warp beam is driven by means of a stepping mechanism and a stroke changing gear with a slide piece adjustable according to the warp thread tension, at a rate in which the tension of the warp threads remains substantially constant.

Such a mechanism is described for instance in the German patent specication No. 869,324. in contradistinction thereto the invention principally consists in a different design of the variable stroke mechanism for driving the stepping mechanism and is essentially characterized in that the first-named mechanism 'mcludes a connecting rod whose one end portion is linked to a drive adapted to impart to the connecting rod a motion with a movement component reciprocating at least in the longitudinal direction, and that the other end portion of the connecting rod is guided by at least one link on an arcuate path whose center of curvature is a pivot through which the linlt is coupled to the slide piece.

An object of the invention is to provide locking parts to exclude any reaction of the stepping mechanism drive from reaching a regulating roller for determining the tension of the warp thread.

Further features of the invention will appear from the following description and ciaims, taken in conjunction with the accompanying drawing with reference to which the invention is disclosed hereinafter purely by way of example.

in said annexed drawing:

FIG. l shows a first form of embodiment of a Warp let-oif motion partly in side view and partly in cross-- section taken on the line l-i of FIG. 2;

FIG. 2 is a vertical cross-section talzen on the line ll- II of FG. l;

FlG. 3 re resents a sectional View of a detail of the same mechanism, taken on the line lli-1H of FIG. l;

FEG. 4 shows a part of the mechanism on a larger scale, partly in top View and partly in horizontal section on the line 1"] IV of FiG. l;

FIG. 5 shows an elevation of `a detail of the mechanism, on a still larger scale;

FIG. 6 shows diagrammatically and in side view a second form of embodiment of a let-ofi motion, whereby numerous parts corresponding to the iirst form are omitted;

FlG. 7 is a similar representation of a third form of embodiment;

FIG. 8 shows .a sectional view taken on the line Vill- Vlll of FIG. 7;

FIG. 9 shows in diagrammatic side view a fourth form of embodiment, numerous parts of the mechanism corresponding to the first form being again omitted.

Referring more particularly to FIGS. 1 and 2, the machine frame il of the loom has laterally attached thereto a bearing piece 1 on which a bearing plate 2 is mounted. lournaled in the bearing piece 1 and bearing plate 2 is a shaft 3 which, by means of a hub 4, firmly carries a toothed wheel 5. The latter is coupled through additional toothed wheels 5, 7 to a shaft (not shown) of the loom. The hub 4 possesses a ange 8 to which is secured a disk 9. Between disk 9 and ange 3 is a ring 10 clamped eccentrically to said spindle 3. By means of screws 11,

3,122,172 Patented Feb. 25, 1954 said disk 9 is drawn towards said ring and 'lange, the screws protruding inside through the ring 10. Ring 1) forms an eccentric for a connecting rod 12 which at one end is carried thereon. The eccentricity of said ring is ice .adjustable within certain limits.

Through a pivot 13, one end of two links 14 is pivoted to the other end of the connecting rod 12. The other end of the two links 14 is connected through a further pivot 15 to a slide piece 16 which, by means of the two guide rollers 17, is displaceably guided on the inner and outer circumference respectively of an arcuate guide 18 firmly attached to bearing plate 1. The axis of roller 17 arranged on the concave side of the arcuate guide coincides with the pivot axis of pivot 15. Therefore the pivot 15 is arranged unsymmetrically with respect to the longitudinal axis of the arcuate guide 1S. The slide piece 16 on the arcuate guide 18 cannot therefore be displaced by forces exerted by the two links 14 on the slide piece 16 because such force jams or binds the latter on the arcuate vguide 18 through rollers 17. To displace the slide piece 16 on the arcuate guide 18 use is made of a pivoting arm 2i?, which pivots on a spindle 19 fixed on the bearing plate 2. The spindle 19 is in the center of curvature of the arcuate guide 1S. The free extremity of arm Zii engages with the slide piece 15 exactly in the center between said two rollers 17, hence symmetrically with respect to the longitudinal axis of the arcuate guide. The arm 2i) is therefore capable of displacing the slide piece 16 on the arcuate guide 1S, without the latter swingirn7 and jamming on the arcuate guide 18.

A cable 21 is attached with one end to lever 20 and with the other end to one arm of a two-armed lever 22. The latter can pivot about a spindle 23 on the loom frame 9. A torsion spring 24 surrounding the spindle 19 is joined thereto at one end and at the other end to the bearing plate 2, and tends to swing the lever 20 so as to cause the cable 21 to move downwards. The other arm of ever 22 carries a regulating roller 25 over which run the warp threads 26.

The connecting rod 12 has pivoted thereto one end of a push-pull rod 27, whose other end is linked to a lug 29 on a control casing 3d by means of a ball-and-socket joint 2S (FIGS. l and 4). The control casing Si? is rotatably mounted on a hollow shaft 31 and accommodates a ratchet wheel 32 rigidly mounted on said hollow shaft. rhe circumference of the controi casing 30 has a plurality of stud-like pawls 33 distributed therealong equidistantly. The studs 33 are radially movable and are under the action of a coil tension spring 34 which, circumferentially of the control casing, is laid Varound all studs 33, keepin(7 them engaged with the teeth of the ratchet wheel 32. The number of studs 33 differs from that of the teeth on the ratchet wheel 32. Preferably the ratchet wheel 32 has one tooth more than there are vstuds 3S. ln this way the same eifect will be achieved, as if the number of ratchet teeth on wheel 32 were multiplied in case only a single stud were present. The parts 30-34 together constitute a stepping mechanism.

The hollow shaft 31 is rotatably supported in mounting 47 fixed to the loom frame 0. Shaft 31 carries a worm 35 which meshes with a Wormwheel 36. The wormwheel 36 is rotatably arranged on a hub 37 and provided with internal teeth 38. The hub 37 has rockably arranged thereon a pawl 3h which, by a closely wound coil spring 40, is held in engagement with the teeth 38. The spring 40 has one of its ends rigidly connected to the pawl 39, the end being set in a bore radial to the swinging axis of the pawl. The spring extends partially around a peripheral groove 41 on a spindle 42, and has its other end firmly secured. Rotation of the shaft 42 frictionally biases the spring to pivot the pawl 39 around the hub 37. Through 3 a reduction gearing 43, 44, said spindle 42 is in engagement with the spindle 45 of the warp beam 46 which is rotatably supportedon mounting 47 and a similar bearing part on the other side of the loom.

The hollow shaft 31 has a shaft 48 which is mounted therein for rotation and endwise displacement and fitted with a handwheel 49. The lower end of shaft 4S carries a dished control member 5t? with an upturned rim exhibiting a sloped lifting face which cooperates with suitably sloped lifting faces of the studs 33. The ratchet wheel 32 and control member 5t? have arranged therebetween a coil compression spring 51 which invariably tends to draw the shaft 43 downwards. The arrangement is such that with an axial displacement upwards of the shaft 4S, the rim of the control member 5t? pushes the studs 33 radially outwards and thus disengages them from the teeth of the ratchet wheel 32. For the axial displacement of the shaft upward, there is provided the device represented in PEG. 5. On the hollow shaft 31 is fixed a jawed sleeve 52 which surrounds the shaft 4S and which during the rotation of the shaft 4S, raises or lowers the shaft 4S, according to the direction of the rotation and connects it with the hollow shaft 31 after a certain rotation. For this purpose the sleeve 52 has two jaws 53, between which are recesses defining helical cam profiles 54. On the shaft 48 two rollers 56 are arranged diametrically opposed to one another, and mounted for rotation on a pin 55 transversely fixed through the shaft 48. These rollers and the cam proles 54 are biased into engagement by the spring 51 pressed against the oblique areas 54. When the shaft 4S rotates with respect to the hollow shaft 31 and the sleeve 52, the rollers 56 move on the cam proiile 54, causing a raising or lowering of the shaft 4S.

The action of the described mechanism is as follows:

With the loom in operation, the shaft 3 rotates with the eccentric arranged thereon. Thus the connecting rod 12 performs a movement which is determined not only by the eccentric 10, but also by the links 14, especially by the position of the pivot 15. When the slide piece 16 is in its lowermost position as indicated by dash-dotted lines, the rod 12 is principally guided only upwards or downwards by means of the links 14. Thus the pushpull rod 27 practically receives no movement component in the horizontal direction, so that the control or ratchet casing remains unaffected and the spindle 45 of the warp beam 46 is not turned.

If then, on weaving, the tension of the warp threads 26 increases, which may take place due to the progressive weaving process as also by the decrease in the coil diameter of the warp beam 46 as well as by temperature and humidity inuences, the regulating roller will be pressed downwards by the action of the warp threads against the action of spring 24. The arm 20 will then be pivoted upwards by the cable 21 and thus cause the slide piece 16 to move upwards along the arcuate guide 18. In this way, the position of the pivot 15 changes which brings about a diiferent movement of the lower end of connecting rod 12 so as to induce also a movement component in the horizontal direction. The more the slide piece 16 is pushed upwards, the greater will be the horizontal movement component of the pivot 13, and thus also the endwise excursion of the push-pull rod 27. During one revolution of the shaft 3, the push-pull rod 27 performs one reciprocatory movement, whereby the control or ratchet casing 30 is rotated forwards and backwards. Upon rotation of the control casing 30 in one direction, the ratchet wheel 32 also will be carried along by means of the stud-like pawls 33, and thus the hollow shaft 31 with the worm 35 be rotated accordingly. Incidentally, via wormwheel 36, pawl 39, shaft 42 and reduction gearing 43, 44 also the spindle 45 of the warp beam 46 will be turned so as to nullify the previously mentioned increase in the warp thread tension.

With normal weaving process, the slide piece 16 takes up a middle position on the arcuate guide 18 so that not only an increase in tension of the warp threads, but also a decrease can be regulated automatically in that the warp beam is driven slower accordingly. It may be added that the characteristic of the spring 24 is such that in the readjustment of lever 22 resulting during regulation, the tension of the spring remains practically unchanged.

If, With the loom at rest, some manipulations shall be carried out, the position of the Warp beam 45 must be capable of being changed by hand. If it is required to turn the warp beam in the way of slackening the warp threads 26, this may be done simply by actuating the handwheel 49, the jawed sleeve 52 being turned by means of the rollers 55, which in turn is rigidly connected to the hollow shaft 31. This turning of the hollow shaft is possible despite the stationary ratchet casing 3i), because the teeth of the ratchet Wheel 32 will then slide over the base of the ratchet studs 33. Turning the other Way in the sense of tightening the Warp threads 26 is at first impossible, because the studs 33 lock the ratchet wheel 32. But in that case in the described construction the pawls 33 automatically are disengaged from the teeth of the ratchet wheel 32 because, as the shaft 4S starts to turn, the rollers 55 move up the cam profile 54, the shaft 43 thus being moved axially upwards against the action of spring 51 which results in the control member 5t) pushing all pawls 33 outwards to disengage them from the ratchet wheel 32. Striking of the rollers 56 on the vertical counterllanks of the jaws 53 causes the jawed sleeve 52 with the hollow shaft 31 to turn, which movement is transmitted onto the warp beam spindle 45. On releasing the handwheel 49, the pawls 33 automatically return to their original position between the teeth of the ratchet wheel 32.

If it is required to turn the beam 46 to a greater extent in the direction of slackening the threads 26, the pawl 39 may be brought out of engagement with the toothing 38 by disengaging the spring 40 from the groove in spindle 42 and re-inserting it thereinto on the opposite side of said spindle.

The automatic regulation range of the described mechanism suices to keep constant the warp thread tension, as the warp beam diameter decreases in operation from maximum to minimum. In order to be able to process various kinds of fabrics with diiferent numbers of picks per unit length, it is necessary to have another possibility 0f adjusting the stroke of the control rod 27. For this purpose, the eccentricity of the eccentric 10 may be adjusted upon slackening the screws 11.

The regulating device described provides that the forces applied to the links 14 do not cause any displacement of the slide piece 16. Such a displacement of the slide piece 16 would cause a displacement of the regulating roller 25 and thus an undesired reaction on the tension of the warp threads. As already stated above, the slide piece 16 cannot be displaced by the links 14 because, under the unilateral force effect of the links 14, the slide piece jams on the arcuate guide 1S. The necessary displacement of the slide piece 16 is accomplished by the lever 20 which engages in the center of the slide piece 16 so that the latter cannot now jam on the arcuate guide 18. Displacement of the slide piece 16 must take place at a time when there are no forces on the links 14 thus jamming the arcuate guide 16. When this is the case, there can be no displacement of the arcuate guide 16 on the arcuate guide 18, and the cable 21 must be elastic in order not to break when lever 20 and links 14 are actuated simultaneously to displace the guide contact 16.

The angular position of the eccentric 10 may advantageously be adjustable in relation to the other movable parts of the loom, in order that the operating instant of the warp let-off motion may be altered with respect to the crank movement for driving the sley.

The embodiment shown in FIG. 6 differs from the aforedescribed one in some points. Instead of the arcuate guide 18 there is now provided a linear guide 113 having a slide piece 116 movably guided thereon. A cable 121 is directly attached to a pin 160 on the slide piece and is so directed by a guide roller 161 that the force exerted by the cable 121 onto the slide piece 116 is al'ways directed parallel to the longitudinal axis of the guide 118. Moreover, the pin 16@ is situated with respect to the longitudinal axis of the guide 118 at a symmetrical point on the slide piece 116 so that the force exerted by the cable 121 cannot cause any locking of the slide piece on the guide 118. A tension spring 124 is also attached with one end to the pin 166 and is anchored with the other end to a fixed point 162. The pulling action ot spring 124 extends in continuation of the cable 121 in order to draw the slide piece 116 towards the other end of the guide 118.

As in the rst form of embodiment, two parallel links 114 are joined through a pivot 115 to the slide piece 116 and through a pivot 113 to one end of a connecting rod 112 which is also connected through the push-pull rod 127 to the stepping mechanism (not shown in FIG. 6) for driving the warp beam, as in the irst form. Through a pivot 163, the upper end or the connecting rod 112 is linked to one arm of a two-armed lever 164 which is pivoted on a stationary bearing piece 1m. The pin 165 may be selectively set in diierent holes 166 in lever 164 in order to change the length ratio of tre two arms of ever 16d. "l" he other arm of lever 164 carries a follower roller 167 which engages an endless control groove 168 in a camdisk 169. The latter is mounted on a shaft 163 (similar to that already mentioned in the rst form) as driven from the loom.

The action of the mechanism just described is substantially the same as in the first form. There is, however, a difference in the drive of the connecting rod 112. Upon rotation of the camdisk 169, its control groove 16d irnparts to the lever 164i a reciprocatory rocking movement about the pin 165. Incidentally, by means of the hinge 163, the upper end of the connecting rod 112 is moved up and down on a circular arc so that said end receives a movement with a major component in its longitudinal direction. rhe movement of the lower end of the connecting rod 112 through the links 114 and the effect thereof upon the push-pull rod 127 are the same as described with respect to the iirst form. By displacing the pin 165, the device may be adapted to various densities of the weft (orC the fabric to be produced), this corresponding to the adjustment of the eccentricity of eccentric 1G in the lirst form.

ln the third form of embodiment according to FGS. 7 8, there is again a rectilinear guide 213 for a slide piece In this case the guide 213 is a round bar and the slide piece 216 has a displaceable sleeve thereon which, however, is provided with a bracket 27). For dis .acing the slide piece 216 along the guide 213, there is provided an arm 22% which can pivot about an axle 219 and has an elongated slot engaged by a pin 26) of the slide piece 215. instead of a cable 21, there is provided a linkage 221 for operatively connecting the arm 22%, and thus the slide piece 216, with the movable backrest roller (not shown in FiG. 7)

Through a joint pin 215 which, with respect to the longitudinal axis of the guide 21S, is unsymmetrically arranged on the bracket 271i of the slide piece, the latter is connected to two parallel links 214 which, in turn, are joined through a pivot 2.13 to the other end of a connecting rod 212 which, via push-pull rod 227, cooperates with the stepping mechanism (not shown) to drive the warp beam. The upper end of the connecting rod 212 is carried on a crankpin 219 which can be adjusted and fixed in a radial slot 266 in a crankdisk 269. The latter is mounted on the shaft 3 driven by the loom mechanism. Fthe joint pin 215 carries a guide roller 275 (PEG. 8) which is guided in an arcuate slot 276 of a plate 277. This plate is attached (in a way not shown) to a station- 5 ary bearing part of the unit and also carries the guide 218. The bracket 27? exhibits an elongated slot 278 through which passes the joint pin 215. The remainder or" the mechanism (not shown in FIGS. 7 and 8) is identical with that in the tirst form.

The action of the mechanism just described is entirely similar to that ot the rst form of embodiment and need not be explained here in greater detail. The forces exerred onto the slide piece 216 via linkage 221 and arm 22@ enables the slide piece to get displaced along the guide 21S without Cn the other hand, any forces exerted upon the slide piece 216 through the links 214, which would cause the slide piece to shift, automatically ei'lect jamming of the same by ratchet action. Through the crankpin 210 a circular movement is imparted to the upper end of the connecting rod 212 as in iirst form through the eccentric 1u. By adjusting the crankpin 21% in the slot 266 the crankarm can be altered for the purpose of adapting the control movement, transmitted through rod 227' onto the stepping mechanism, to the density of the weft of the fabric being produced.

The fourth form of embodiment according to Flf. 9 again includes, for driving the connecting rod 212, a crankpin 21S winch can be adjusted and xed in a radial slot of a crankdisk 269. As the previous forms, the lower end of the connecting rod 212 is joined through a pivot 313 to a link 314 and to the push-and-pull rod 327 leading to the stepping mechanism (not shown). The other end of link 31d is joined through a pivot 31S to a slide piece 316 which essentially is an arm pivotal about a stationary pin 319. immediately adjacent to the slide piece 316 there is a cylindrically shaped guide 31S. `Radialiy outside latter, the slide piece 316 includes a laterally proje ting casing-like part 380 which is open towards said guide. Located between the guide 318 and the casing-like part iltl there are two rollers 381 acting as locking members whose spindles are drawn towards each other by at least one spring. The rollers 331 thereby get jammed between guide 31S and casing-like part 330, thus bringing about a locking action which prevents movement of the slide piece 316 in either direction. Moreover, the pin 319 has pivoted thereon a lever 32@ which, through a linkage 221, is adjustable from the backrest (not snown in PEG. 9) according to the warp tension. ri`he rree end oi lever 3243; carries a member engaging between the two rollers 331.

As in the case of tue previously described examples of execution, the slide piece 316 cannot be displaced by the link 31d but only by the lever 325i on the arcuate guide 318. The blocking action is as follows:

When the link Sie tries to displace the guide contact 316, one of the two rollers 381, according to the direction of the movement, is jammed in between the cam proiiles of the housing 33% and the arcuate guide 313. However, the arcuate guide 318 is to be displaced vith the aid of the rod 221 and the lever 329, the blocking action of the two rollers 381 is avoided. At nrst, the lever 32:3, according to its swinging direction, strikes against one of the rollers 331 and pushes it out of reach against the bias of the spring 2 in which it might be jammed between the cam profiles 339e of the housing and the arcuate guide 31S. With the further movement of the lever 32d, the latter displaces the slide piece 1o by striking over the roller 3%1 against the housing di 'acing the same together with the slide piece 316 on the arcuate guide 31S.

lt is understood that the warp tension may also be determined by a movable member other than a back rest roller 25 (F1-G. l) adjustable in a parallel manner. Such devices for feeling out the warp tension are too familiar to need description.

The handwheel 49 (FlG. l) arranged to adjust the warp beam by hand need not in each case be located beside the warp beam bearing. lt is possible and preferable to have this handwheel mounted at the front of the loom, within convenient reach by the operative, so that she or he can carry out manipulations on the warp beam without having to leave the working place.

What l claim is:

1. In an automatic let-off for looms having a regulating roller mounted for determining the tension of warp thread and having a warp beam driven by a stepping device and a stroke-changing gear with a slide piece adjustable according to the warp thread tension, at a rate in which said warp thread tension remains substantially constant, an improved mechanism for driving the stepping device comprising a connecting rod whose one end portion is linked to a drive adapted to reciprocate said rod with movement components ranging between the vertical and the horizontal, a link having its ends respectively pivoted to the other end portion of said rod and to said slide piece, whereby the other end portion of said rod is guided on an arcuate path Whose center of curvature is the end of the link pivoted to the slide piece.

2. Mechanism according to claim 1, wherein an arcuate guide is mounted adjacent said drive, and extending for approximately a quadrant therearound, for slidably mounting said slide piece thereon, said slide piece having respective ends extending transversely beyond the respective sides of said arcuate guide, a ratchet means mounted on the respective ends of said slide piece, said slide piece being connected to said link by one of its ends nearest thereto, and being connected at its center through means to a regulating roller whereby forces transmitted to said guide through said link actuates said ratchet means to lock said slide piece against displacement and forces from said regulating roller do not actuate said ratchet means to lock against displacement by said regulating roller.

3. Mechanism according to claim 2, wherein the slide piece embraces said arcuate guide, and the pivot joining the link to said slide piece being arranged at a radial distance from Vsaid arcuate guide whereby the forces transmitted by said link onto said slide piece cause the latter to tilt on the arcuate guide, whereas said means connecting the regulating roller to the slide piece are joined t0 the latter in the transverse center of the arcuate guide.

4. Mechanism according to claim 3, wherein the slide piece includes a casing-like part with two inner inclined surfaces, which is open towards the arcuate guide, two locking members mounted in said casing and adapted to clamp themselves by ratchet action between the arcuate guide and two inner inclined surfaces of said part to lock the slide piece against displacement in either direction, a lever connected to said regulating roller and cooperating with said locking members whereby movement of the regulating roller, pushes one or the other locking member into a nonlocking position for the purpose of nulliiying the ratchet action and readjusting the slide piece.

5. Mechanism according to claim 1, wherein an axially displaceable shaft tted with a haridwheel for turning the warp bearn by hand is connected lthrough a jaw coupling with a coaxial shaft and stepping gear which operates with a ratchet wheel to drive the warp beam, said coupling permits a limited relative movement of said shafts circumferentially thereof and includes at least one helically extending control cam proijle and a roller cooperating therewith, whereby turning said handwheel in one direction, the shaft is axially displaced, a plate with an upturned rim carried by said axially movable shaft, cooperates with sloped run-up pawl faces of pawls of the steping gear in order to disengage said pawls from the ratchet wheel to thus nullit'y the action of the stepping gear.

References Cited in the le of this patent UNITED STATES PATENTS 917,682 Toyoda Apr. 6, 1909 1,749,120 Baker Mar. 4, 1930 1,987,864 Nogamy Jan. 15, 1935 2,585,167 Picanol Feb. 12, 1952 2,609,007 Beall Sept. 2, 1952 2,914,093 Anderson et al Nov. 24, 1959 

1. IN AN AUTOMATIC LET-OFF FOR LOOMS HAVING A REGULATING ROLLER MOUNTED FOR DETERMINING THE TENSION OF WARP THREAD AND HAVING A WARP BEAM DRIVEN BY A STEPPING DEVICE AND A STROKE-CHANGING GEAR WITH A SLIDE PIECE ADJUSTABLE ACCORDING TO THE WARP THREAD TENSION, AT A RATE IN WHICH SAID WARP THREAD TENSION REMAINS SUBSTANTIALLY CONSTANT, AN IMPROVED MECHANISM FOR DRIVING THE STEPPING DEVICE COMPRISING A CONNECTING ROD WHOSE ONE END PORTION IS LINKED TO A DRIVE ADAPTED TO RECIPROCATE SAID ROD WITH MOVEMENT COMPONENTS RANGING BETWEEN THE VERTICAL AND THE HORIZONTAL, A LINK HAVING ITS ENDS RESPECTIVELY PIVOTED TO THE OTHER END PORTION OF SAID ROD AND TO SAID SLIDE PIECE, WHEREBY THE OTHER END PORTION OF SAID ROD IS GUIDED ON AN ARCUATE PATH WHOSE CENTER OF CURVATURE IS THE END OF THE LINK PIVOTED TO THE SLIDE PIECE. 